Friday, March 12, 2010

Determining when a poa annua seedhead will attempt to form in the plant

That's the question many superintendents are pondering at this moment.  When should I apply the control products to my greens to reduce the effects of poa annua seedheads?(Click on poa annua for great power point regarding this weed)  One of the great benefits of bentgrass which is the plant that we want to be the dominant species on our greens is that it does not form seedheads at green heights of cut.  Poa annua on golf greens can continously produce seedheads from the beginning of spring until temperatures near 90 begin to invade our area in June.  Greens being cut under .125" can become very bumpy from this prolific seeder.  Verticutting, grooming, sanding, and dragging greens can reduce the impacts of seedheads slightly but the most effect seedhead control comes from Plant Growth Regulators which prevent the seedhead from  forming in the first place.  

We use a combination of two Plant Growth Regulator chemicals which does reduce the amount of seedheads to a more acceptable level than not applying the products at all.  This combination spray is variable in its working ability but is less harmful than other regulators which can effect the bentgrass more severely by discoloring and possibly thinning the turf.

Rough height poa in full seedhead glory!
We use a model for growing degree days to help us determine the best time to apply our products. 
Growing degree days are determined by the measurement of daily average air temperatures. Farmers, horticulturalists, and superintendents utilize past research which has studied how temperature affects certain weed, insect and disease pests. A specific cycle of life of a pest is signaled when a cumulative number of growing degree days are reached. i.e. Poa annua forming seedheads.

We have been monitoring a website which is assists us in measuring growing degree days. Growing degree day models use scientific research and studies which help to determine when seedheads will begin the process of forming within the crown of the plant.  Proper timing of applications equals the best opportunity to be effective at managing the production of seedheads. 

We begin to measure growing degree days as of March 1st in our area.  The average daily temperature is
measured and is then subtracted from a base temperature model.  There are two base models used  depending upon the intended pest that you are trying to control and the product you are wanting to use.  The models are based on 32 and or 50 degree temperature base.   

We are using the 32 degree model for our Primo/Proxy regulator application.  Below is an example of how we determine the growing degree for a specific day.

GDD = Growing Degree Days

March 11   High Temp       67     
                   Low Temp        47     
                   Average Temp 57     
Avg Temp       57
GDD Base   - 32                                                      
                       25 GDD for March 11

We then add 25 to the total number which has been accumuating since March 1st.  At this time, our current growing degree model is showing Cahokia, IL which is the second dot from the bottom of Illinois at around 148 growing degree days.  Our model calls for our spray application to be made around an accumulation of 200-250 growing degree days or slighly sooner based on  research recommendations.

We had intended to make our application on March 12th but with rain in the forecast could reduce the effectiveness of the application.  We will be making our first application this Monday based on this model and must do a repeat application in 3 weeks to give us the best control possible.  One of the products we are using takes 7-10 days to become fully active in the plant.  The trick to get the best control is to insure that seedheads have not begun to form in the base of the plant.  If it has, we have missed the initial window but will still get some control.  It is important to be slighly early than late according to research recommendations.  Also, a plant will produce many seedheads during the spring season so goes the ability to get some control if the earliest window is missed.

In an earlier blog, I mentioned a growth regulator for slowly reducing the amount of poa annua in our greens  This material will also help to reduce the effects of poa annua seedlings that do germinate by reducing its growth and keeping it tighter to the canopy of the green which will allow the ball to roll more smoothly.

I found an interesting article in the USGA archives talking about poa annua and how it was being eliminated back in 1927 on a particular course.  Click on the USGA link above for an interesting read.  We've been fighting this weed for a long time.

During this process,, you might notice some greens that have less poa seeding such as 2, 3, or 11 because their overall poa population is much less than greens like 1 or 17 which are more heavily infested.

1 comment:

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